This invention relates to an improved inorganic fiber mat useful inter alia as a felt for roofing products, such as asphalt shingles. The invention further relates to a process and apparatus for making such an inorganic fiber mat or sheet containing mineral wool or a combination of mineral wool and other fibers, such as fiberglass, whereby greatly improved properties are attained by use of a novel cleaning system for the mineral wool fiber.
In recent years, there has been a marked increase in the use of inorganic fiberglass mat in place of the conventional organic felt base, made traditionally of cellulosic fibers, in the preparation of roof and floor sealing products. The terms "fiberglass" and "glass fiber", as used herein, refer to fibers of silica materials which are formed through an extrusion process. Such fibers are generally of uniform diameter and relatively free of non-fibrous contaminants. In order to form a fiberglass mat, a "wet-laid" process is often used whereby the glass fibers are mixed with water to form a relatively thick slurry, which is then fed to a dispersion tank. The slurry is diluted in the dispersion tank with water, and optionally with a small quantity of a dispersing agent to facilitate the separation of the fibers. The slurry is mixed in the dispersion tank to form a relatively uniform mixture. The mixture is pumped to a head box, which lays a uniform dispersion on a moving screen to form the glass mat. Water is suctioned through the forming wire into the machine white water tank, from which it is recycled in the process. Unlike cellulosic fibers which are self-adhering upon wetting, glass or any inorganic fibers require an organic resin binder to form a mat useful for conversion into roofing products. As such, the glass or inorganic fiber layer as formed on the screen is thereafter impregnated with a binder, such as a urea formaldehyde or a urea formaldehyde-latex blend. Other binder systems can be used as needed for various products selected by those skilled in the art.
While fiberglass does produce a fiber mat having excellent tensile strength, flexibility, and dimensional stability, glass fiber is relatively expensive to manufacture, especially in view of recent increases in the cost of energy. It would, therefore, be desirable to utilize substitute inorganic raw materials which can be fiberized and have characteristics similar to those of fiberglass, but which are less costly. It has long been known that mineral fibers can be prepared from various silicate based inorganic raw materials using a process in which the raw material in molten form is "blown" or "spun" into fibers. These products are commonly referred to as "mineral wool", which is a generic term for various mineral fibrous materials commonly known as "rock wool", "slag wool" and "glass wool". Rock wool is made from natural rock or combinations of natural minerals; slag wool is derived from iron, copper or lead blast furnace slag; and glass wool is made from conventional glass batch materials such as silica, sand, soda ash or borax, dolomite, and minor ingredients.
While mineral wool is prepared in a fibrous form, its applications are limited as compared with fiberglass since by known methods for preparing mineral wool, it has a substantial content of non-fibrous contaminants in the form of grit, sand, large shot, and fines. Typical mineral wool contains up to about 30-60% of such contaminants. In addition, the fibers themselves have random diameter distribution and tend to have pieces of shot adhered at the end of the fibers.
The non-fibrous or particulate contaminant materials are undesirable because they reduce the mechanical strength of the mineral wool. Moreover, the particulate material can be so fine as to become air-borne as dust, and become distributed over a wide area. Since the dust can cause skin irritation and other injuries, particularly if inhaled, this can pose a considerable problem during conversion of mineral wool into other useful products. Consequently, it is desirable that the non-fibrous contaminants be removed, but this has heretofore been difficult to accomplish. Since the contaminant material is made of the same material as the fibers, the contaminants cannot be dissolved out, nor does a sufficient amount of the contaminants have a different density as compared to the fibrous material which would facilitate satisfactory separation by other techniques. Moreover, the brittleness of the fiber precludes any relatively rough treatment which might cause the fibers to be crushed, broken or otherwise destroyed.
Accordingly, the relatively "dirty" mineral wool heretofore known in the art is at best a poor substitute for glass fiber, and, as such, its primary use has been in batt form as insulation. Prior attempts to incorporate mineral wool in anything but a minor proportion in other fibrous based products, such as roofing felt, have been unsatisfactory. More specifically, with regard to roofing products, the large proportion of shot and other contaminants (which are of a different configuration than the fiber), as well as the relatively brittle nature of the fibers, result in a mat or sheet having a lower tensile strength since the adhered shot in the fiber portion causes an overall weakening. In a conventional commercial wet-laid process for preparing a mat from mineral wool, the high degree of contaminants interferes with the binder such that proper bonding of the fibers is not satisfactorily achieved. The non-fibrous contaminants are carried along with the machine water during recycling and foul the processing equipment, particularly the mat forming wire or screen, thus necessitating frequent shut downs, cleaning, and equipment maintenance.
Numerous attempts have been made to refine or clean mineral wool so as to separate and remove the non-fibrous contaminants from the raw fiber. No prior process or method has been entirely satisfactory or commercially acceptable, particularly for producing mineral wool fibers suitable as a satisfactory fiberglass substitute. These prior methods have included a wide range of separation processes, equipment and techniques based upon simple mechanical agitation, washing, a gaseous fluid bed or stream, a gas cyclone and various combinations thereof. Typical prior art techniques are described in U.S. Pat. Nos. 3,055,498; 3,111,719; 3,142,869; 3,308,945; 3,865,315; 4,229,285; 4,268,294; 4,269,701. These so-called "cleaning" processes for mineral wool as known in the art include both "dry" and "wet" cleaning apparatus. In a dry process, a high proportion of the useable fibers can be lost, rendering such a process uneconomical. In addition, there are various environmental hazards to be considered, since most processes involve spinning the fibers in air. In the various known processes for wet cleaning of mineral wool, the fibers are suspended in an aqueous medium, which is agitated such that the fibers tend to rise and the shot and other particulate contaminants, due to differences in relative surface area vis-a-vis the fiber, tend to settle. Such processes often incorporate various abrading means so as to attempt to break off the "adhered" shot from the ends of the fiber, and thereby produce a cleaner fibrous material. Substantial quantities of the fiber are often lost by this technique. In addition, in many of the prior wet processes, when the cleaned mineral wool is recovered and dried, it is difficult, when re-slurrying, to achieve a separation of the fibers. The fibers instead tend to intertwine and remain in clumps.
Accordingly, it is an object of this invention to provide an improved inorganic fiber mat, and in particular a mat containing mineral wool fibers, which is sufficiently and substantially free of non-fibrous contaminants.
It is also an object of this invention to provide an inorganic fiber mat containing mineral wool which is an acceptable fiberglass substitute in the manufacture of mat and sheet materials suitable for use inter alia as roofing felt or otherwise as a sealing membrane for building and other industrial uses.
It is a further object of this invention to provide a method and apparatus for the effective separation and removal of non-fibrous contaminants from inorganic fibrous material at minimal cost and without any substantial fiber damage or diminution of the physical properties of the fiber.